1. Field of the Invention
This invention generally relates to a bicycle rim for a bicycle wheel. More specifically, the present invention relates to a bicycle rim, which is configured to improve the roundness of the bicycle wheel when the spokes are placed under tension between the rim and the hub.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has also become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One particular component of bicycles, which has been extensively redesigned over the past years, is the bicycle wheel. Bicycle wheels are constantly being redesigned to be lightweight and more aerodynamic in design as well as to be simple to manufacture and assemble.
There are many different types of bicycle wheels, which are currently available on the market. Most bicycle wheels have a hub portion, a plurality of spokes and an annular rim. The hub portion is attached to a part of the frame of the bicycle for relative rotation. The inner ends of the spokes are coupled to the hub and extend outwardly from the hub to the rim. The annular rim is coupled to the outer ends of the spokes and has an outer portion for supporting a pneumatic tire thereon. Typically, the spokes of the bicycle wheel are thin metal wire spokes that are placed under tension. Each end of the hub is provided with a flange that is used to couple the spokes to the hub. In particular, holes are provided in the hub flanges. The wire spokes are usually bent on their inner end and provided with a flange that is formed in the shape of a nail head. The inner ends are supported in the holes in the hub flanges. The outer ends of the spokes typically are provided with threads for engaging spoke nipples, which secure the outer ends of the wire spokes to the rim. In particular, the spoke nipples have flanges, which engage the interior surface of the rim. Alternatively, the spokes may be reversed, with the outer end having the nail head and the inner end having the threads for engaging the spoke nipples, which secure the inner ends of the wire spokes to the hub.
Typically, conventional spokes are attached to either the inner edge or the lateral side portions of the rim. Thus, the amount of force that can be applied to the rim by the spokes depends mainly upon the thickness of the inner edge of the rim or the lateral side portions of a rim. In order to accommodate the stress from the spokes, the inner edge of the rim can be made thicker. However, making the rim thicker increases the weight of the rim.
In recent years, wheels have been designed with reinforcing members arranged on the outer ends of the spokes to aid in disbursing the stress concentrated on portions of the rim. Such a wheel is disclosed in Shimano""s U.S. Pat. No. 6,126,243. This wheel (i.e., rim, and spoke combination) is very strong, lightweight, and relatively simple and inexpensive to manufacture.
Generally speaking, the spokes in the bicycle wheel must be applied with a certain amount of tension in order to provide rigidity and trueness to the wheel. In conventional style wheels with thirty-two or more spokes, the tension applied on any one spoke is not very great. Moreover, the spokes pull the rim relatively evenly because the spoke attachment holes in the rim are fairly close together.
However it is desirable in the bicycle industry to have as few spokes as possible. One problem with reducing the number of spokes is the concentrated stress applied to the rim. In other words, if fewer spokes are used, the stress on the rim by each spoke becomes increasingly larger. Therefore, the spokes in the wheel with fewer number of spokes pull the rim with greater force at each attachment point. This typically causes greater deformation of the rim at the spoke attachment points than the remaining sections of the rim. Thus, the wheel after being assembled may not be truly round. In other words, the outer peripheral edge of the rim can be deformed into a somewhat polygonal shape. For example, bicycle wheels have been produced with sixteen spoke attachment portions with a pair of spoke attachment portions being positioned very close to each other. When tension is applied to the spokes, the rim is deformed from a substantially perfectly round shape to a polygonal shape after assembly of the wheel.
In view of the above, there exists a need for a bicycle rim that overcomes the above-mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
One object of the present invention is to provide a rim in which tensioning of the spokes produces a bicycle wheel with improved the roundness.
Another object of the present invention is to provide a rim that can be manufactured without substantially increasing the cost of manufacture.
Yet another object of the present invention is to provide a rim that can be utilized with a low number of spokes.
The foregoing objects can basically be attained by providing a bicycle rim that comprises first and second annular side portions, an inner annular portion, an outer annular tire attachment portion and a plurality of circumferentially spaced spoke openings. The inner annular portion is disposed radially inwardly of the first and second annular side portions and disposed axially between the first and second annular side portions. The outer annular tire attachment portion is disposed axially between the first and second annular side portions. The tire attachment portion has non-circular outer peripheral edges arranged about a center axis of the rim. The circumferentially spaced spoke openings are formed in at least one of the following: the inner annular portion or the first and second annular side portions. The non-circular outer peripheral edges have first radii extending from the center axis of the rim and passing through the spoke openings that are larger than second radii of the non-circular outer peripheral edges passing midway between selected circumferentially adjacent pairs of the spoke openings.
The foregoing objects can also basically be attained by a method of forming a bicycle wheel comprising the steps of: forming a non-circular bicycle rim having a non-circular outer periphery arranged about a center axis of the rim; attaching a bicycle hub to the non-circular bicycle rim by a plurality tension spokes; and tightening the tension spokes to place the tension spokes under tension and deform the rim inwardly in a generally radial direction to become more circular.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.